1. Field of the Invention
The present invention relates to a moving body position detecting method and disc drive apparatus.
2. Description of the Related Art
For example, in a disc drive apparatus capable of reproducing data from a disc such as a CD (compact disc) or a DVD (digital versatile disc), data readout, for example, is performed while control is so made that a desired position on the disc is accessed. In this case, control signals corresponding to a movement speed and a movement distance are generated and a rough movement of an optical unit as a data readout means from a current position to an access position is controlled based on those control signals.
The rough movement is an operation in which a pickup having a laser diode, a photodetector, an objective lens, etc. is moved in the radial direction of the disc by a sled mechanism. In the pickup rough movement control of the disc drive apparatus, position detection is performed based on a rotation operation of a sled motor.
For the pickup position detection, four signals, for example, that are close to a sinusoidal wave and correspond to a rotation operation of the sled motor are generated.
A signal having a maximum value among the four signals is detected. Further, when the maximum value signal has changed to another signal, a prescribed pulse indicating how the maximum value signal has changed is output to, for example, a control means that controls various operations of the disc drive apparatus and the pulse is inverted. Based on pulses received from the maximum value detecting means, the control means can count the number of times of changes of a maximum value signal. A movement distance of the pickup is detected based on this count value.
However, when, for example, noise is superimposed on a signal to be used for maximum value detection, erroneous counting may occur. In particular, when the movement speed of the pickup is low, signals that are compared with each other for maximum value detection vary slowly and hence noise is more easily superimposed thereon. As a result, in signal level comparison, an erroneous comparison result may occur due to influence of noise. Specifically, for a single changing point, two changing points may be detected erroneously due to counting of superimposed noise. Further, an error is added to pickup position detection information every time such erroneous counting occurs.
There may occur a case that the pickup cannot correctly be moved to a desired position when an error occurs in the position detection due to noise or the like.
Further, since only how the maximum value signal changes is detected and the pickup movement direction is not taken into consideration, erroneous counting may occur when the movement direction is reversed during a movement. For example, assume a case that when the pickup is being moved toward the disc outside, certain disturbance causes reversing of the movement direction and a changing point is counted. Since the change in movement direction cannot be detected from this counting operation, this counting operation is performed with a recognition that the pickup is still moving toward the disc outside.
As described above, conventionally, an error may occur in the pickup position detection due to influence of noise, disturbance, or the like, in which case the pickup may not correctly be moved to a desired position. Therefore, when the pickup is moved to a position distant from a desired position due to erroneous counting, the current position cannot be identified until address information or the like that is recorded on the disc surface is read out and checked. That is, to move the pickup to a desired position, it is necessary to move the pickup based on address information that is read out from the disc after moving it based on position detection information. This means execution of a wasteful operation and prevents reduction in power consumption.
The present invention has been made in view of the above circumstances in the art, and an object of the invention is therefore to increase the accuracy of detecting the position of an optical unit.
To attain the above object, the invention provides a method for detecting a position of a moving body, comprising the steps of generating a plurality of periodical signals as the moving body moves, the periodical signals being given respective fundamental values; sequentially detecting a fundamental value of one of the periodical signals that has a maximum value; generating an extension value in such a manner that the extension value is incremented or decremented when the detected fundamental value changes from one unit repetition range to another; constructing position detection information of the moving body as a combination of the detected fundamental value and the extension value; and storing the position detection information.
The invention also provides a disc drive apparatus comprising detecting means for sequentially detecting a fundamental value of one of a plurality of periodical signals that has a maximum value, the periodical signals being generated as a pickup moves that records and/or reads data on and/or from a mounted disc, the periodical signals being given respective fundamental values; storing means for storing position detection information of the pickup as a combination of the detected fundamental value and an extension value, the extension value being incremented or decremented when the detected fundamental value changes from one unit repetition range to another; and control means for controlling movement of the pickup based on the position detection information stored in the storing means.
The moving body position detecting method according to the invention makes it possible to obtain fine position detection information of a moving body by reducing influence of noise or the like that is superimposed on signals.
The disc drive apparatus according to the invention makes it possible to recognize the current position of the pickup in the disc radial direction based on position detection information that is obtained as the pickup moves. The movement control on the pickup can be performed efficiently based on such position detection information.